Medical X-ray transparencies are usually examined by placing them over the viewing surface of a device commonly referred to as an illuminator. Conventional illuminators normally comprise a box-like structure enclosing fluorescent lighting tubes behind a light diffusing plate defining the display area. Commonly, transparencies are retained on the surface of the viewing surface by pushing the upper edge of the transparencies under spring-loaded film-holder clips located along the top edge of the viewing surface.
Standard size illuminators have a viewing surface 17 inches high and 14 inches or multiples of 14 inches (i.e. 28 inches or 56 inches) wide. Usually, each 14 inch width of viewing surface has its own fluorescent tubes and control switch. Such viewing surface enables the viewing of standard size X-ray films which measure up to 17 inches by 14 inches.
The sections of the viewing surface not covered by transparencies need not be illuminated. This eliminates unnecessary glare from areas outside the transparency. When transparencies smaller than 14 inches by 17 inches are to be examined, they are typically retained on the display area in the same manner as full size transparencies, i.e., suspending them by means of the film-holders along the top of the viewer. This leaves a portion of the display area surrounding the transparencies fully illuminated, with the resulting glare detracting from the visual perception of the person trying to study the transparency and assess the information it contains.
Moreover, in many instances, the region of the display area which is of highest interest to the viewer is quite dense. Thus, viewing of the region and assessment of information therefrom may be particularly cumbersome and difficult.
Often transparencies contain several very transparent areas, and, frequently, radiologists have to examine over-exposed transparencies. In these cases, considerable glare emanates through areas of the transparencies themselves.
Attempts have been made in the past to provide viewing devices for X-ray transparencies which shield the eyes of the observer from light other than that passing through the transparencies; to obscure light in parts of the transparencies, and to reduce the contrast in transparencies when so required.
U.S. Pat. No. 1,988,654 to Haag discloses a light box which incorporates two manually movable curtains for masking all of the light-transmitting surfaces of a diffuser up to the edges of a transparency.
U.S. Pat. No. 2,436,162 to Cadenas discloses an X-ray viewer having a masking arrangement incorporating a plurality of hinge-connected opaque masks which may be manually pivoted relative to each other to expose all or only selected parts of an X-ray transparency.
U.S. Pat. No. 4,004,360 to Hammond is directed to a self-masking viewing device which purports to automatically obscure areas of the viewing screen not occupied by the X-ray transparency. In the disclosed device, the screen is provided with a multiplicity of holes which may be selectively blocked by shutters or opened for the passage of light. The interior of the device is connected to a vacuum source which functions to hold the film against the front surface of the device.
The vacuum functions, in addition, to close the shutters connected with those holes not covered by the transparencies, so that passage of light through such holes is prevented. Air cannot pass through those holes in registry with the transparencies and, thus, the shutters associated with the covered holes remain open for the passage of light. The device described is unsuitable for critical inspection of X-ray transparencies since the presence of holes and shutters in the areas in registry with the transparencies creates a pattern behind the transparencies which interferes with the ability to accurately read them.
U.S. Pat. No. 4,373,280 to Armfield discloses an X-ray viewing plate having a cross bar for supporting transparencies at a central portion of the screen. A series of shades is provided which may be manually activated to obscure selected parts of the illuminated surface.
U.S. Pat. No. 4,510,708 to Porkinchak discloses an X-ray viewing device which includes a series of masks on an elongated scroll. In a specific embodiment of the invention, the scroll is moved by a motor on a pair of feed rolls. The masks are sized to correspond with stock sizes of X-ray transparencies. The apparatus has a dimensional sensing mechanism which aligns a selected mask with a positioned transparency automatically in accordance with the sensed dimension. The transparencies are inserted into a film-holder. The widthwise sensing function is performed by a series of levers or fingers positioned to engage an edge of the film.
U.S. Pat. No. 4,637,150 to Geluk describes a system in which a cathode ray tube is used as a light source and the light emitted by this source is modulated in accordance with the stored density of a transparency. This system is impractical due to the limited sizes and associated light intensity outputs of CRTs for this type of illuminator.
U.S. Pat. No. 4,908,876 to Deforest et al., describes, inter alia, a transparency viewer using projection lens to project a light source for backilluminating a transparency.
U.S. Pat. No. 5,313,726 to Yaniv et al., describes a transparency viewer in which a light source, mounted in a reflecting housing, is used to back-illuminate a transparency.
German Patent Application DE 33 31 762 A1 describes an array type electrochromatic illuminator in which back-lighting selectively illuminates portions of a viewing surface in response to the application of voltage to horizontal and vertical strip conductors on opposite faces of an electrochromatic material placed between the source of illumination and the viewing surface.
U.S. patent application Ser. Nos. 07/861,982 and 08/175,372 to Inbar et. al., now U.S. Pat. No. 5,430,964, and PCT Publication WO 93/01564 and WO 91/10152, the disclosures of which are incorporated herein by reference, disclose self-masking transparency viewing apparatus having a mask-pattern generating device which may be an electrically-controlled Liquid Crystal Array (LCA). In addition, there is provided a transparency detection means, such as optical sensors which recognize optical properties, for example, attenuation, on the display area including images within the transparencies and the face of the transparencies themselves. The detection data is transferred to a system control unit which drives the LCA to produce a complementary masking pattern in conformity with the displayed transparencies, masking all other portions of the display area.
From the above-referenced prior art, it will be understood that there has not heretofore been available a device capable of producing an illumination field in conformity with the displayed image-carrying transparencies, with no interposing masking means or apparatus between the light source and the illuminated portions of the transparencies, and which does not require operator assistance to recognize and set the transparency field, or parts thereof, to be illuminated and which is further capable of automatically intensifying the illumination field projected through the displayed image-carrying sections of the transparency.